Such nozzle bodies are sometimes called aperture plates, nozzle arrays, dosing aperture, orifice plate, vibratable membrane member, dosing aperture arrangement, aerosol generator, and the like. These terms are hence to be understood as being interchangeable throughout the present document.
In fact, such nozzle bodies and droplet dispensing devices are well known, for example, see the document EP 1 129 741 in the name of the present Applicant. This document describes a liquid droplet spray device having a top substrate formed of a main body and of a nozzle body. The nozzle body contains a nozzle array of liquid droplet outlet means allowing a liquid substance contained in the liquid droplet spray device to exit the device, in this case as a spray of droplets. The nozzle body is conventionally formed of a nozzle array.
In order to allow for an effortless transportation of liquid out of the reservoir into the nozzle body, a venting hole may be used to ensure correct pressure difference between the inside of the reservoir and the surrounding atmosphere. An example is shown in FIG. 1. A reservoir 3 contains liquid and is covered by a cap in which a venting hole 35 may be provided. A gasket (not shown) may be provided to ensure liquid tightness.
However, if the spray device is, for example, held in an upside down position, liquid may seep through the venting hole 35 shown in FIG. 1 causing leakage and inconvenience, such as unwelcome smell, etc.
Similar leakage can be caused by a change of temperature of the liquid, for example, because of hand holding the device, resulting in a change of volatility of the liquid. Another cause of leakage is increased pressure on the reservoir induced by a hand of a user or by change of atmosphere pressure, wherein the resulting deformation forces liquid to exit the reservoir, and the spray device, by way of the venting hole.
As can be understood from the above, it is thus important to provide a venting hole to ensure correct spraying, but a venting hole causes unwanted leakage of liquids to be sprayed. In room fragrance devices, this is generally not a major problem, because the device is generally positioned on a stable surface and in a stationary position.
However, in a personal fragrance device, for example, a perfume dispenser, such leakage is much more prominent, because the device can put in a pocket or a handbag, and thus may be in any position. Indeed, any perfume leaking out into a ladies handbag, for example, is of course to be avoided.
It is therefore desirable to provide a liquid droplet dispensing device for emitting perfume and the like that is watertight.
However, the design of such a watertight device is limited due to physical laws, in particular, Jurin's rule. Indeed, Jurin's rule defines the height that a liquid can reach when rising in a capillary tube. This rule states that the height of liquid in a capillary tube is inversely proportional to the diameter of the tube at the surface of the liquid only. This rule is as follows:
      h    =                  2        ⁢                                  ⁢        γ        ⁢                                  ⁢                  cos          ⁡                      (            θ            )                                      r        ·        ρ        ·        g              ,
where:                h is the height of the liquid;        y is the surface tension of the liquid;        θ is the contact angle between the liquid and the wall of the tube;        ρ is the fluid density of the liquid;        r is the radius of the tube; and        g is the gravitational acceleration.The valid conditions for applying Jurin's rule are as follows: the diameter of the tube must be smaller than the capillary length, which typically is 2 mm for water at ambient temperature and pressure.        
This means that such a liquid droplet dispensing device has design constraints resulting in a limited height and shape, because liquid can only rise over a limited distance by capillary action. Clearly, in the world of perfume, such constraints are very limiting.
The present invention addresses this contradictory aspect and provides a liquid droplet dispensing device that is watertight and that allows one to overcome the design constraints imposed by Jurin's rule.